Infusion packages for brewing beverages, such as tea bags and coffee bags, are generally produced by enclosing finely ground beverage precursor materials within a porous web material. The beverage precursor materials can include tea, coffee, hot chocolate mix and soup mix. The infusion package is either placed in a cup or pot containing boiling water, or alternatively, the infusion package is placed in an empty cup or pot and subsequently boiling water is added. In either event, the hot water passes through the web material into the bag to extract the beverage precursor materials and the extract passes outwardly of the bag to form the brew.
Infusion packages are generally made from cellulose fiber based nonwoven web materials that are free from perforations or punctures yet possess a high degree of porosity. Particularly favored for infusion packages have been those wet laid fibrous materials made on inclined wire paper making machines using long natural fibers. These web materials are generally soft, tissue-thin fibrous materials characterized by their lightweight and superior infusion characteristics. The fibers used for the production of infusion packages are typically regulated by governing agencies for use as packaging for food products.
While it is desirable for the infusion package to allow extraction of the beverage precursor materials, physical release of the finely ground beverage precursor materials from the sealed infusion package into the cup is undesirable. To prevent movement of finely ground beverage precursor materials from the sealed infusion package into the brewing container, the porosity and “sifting” characteristics of the nonwoven web material are carefully controlled. Importantly, the seam maintaining the beverage precursor materials within the infusion package must maintain integrity to prevent opening of the infusion package and the subsequent undesirable discharge of the finely ground beverage precursor materials into the brew.
Infusion package seams may be of either the “heat seal” or “non-heat seal” variety. In non-heat seal infusion packages, the edges of the web material are brought together, folded a number of times, and this multiple fold is crimped to provide a mechanical crimped seam which seals the infusion package. Typically, the nonwoven web material used for non-heat seal infusion packages includes a single layer comprised of vegetable fibers and does not incorporate fusible polymeric fibers.
Heat sealed infusion packages are typically produced from a wet laid, cellulose based nonwoven material comprising two layers or phases. One of the phases, the heat seal phase, typically includes more than twenty-five percent by dry weight of fusible thermoplastic polymeric fibers. The surface of the second phase, and typically the second phase itself, is substantially free of fusible fibers. The web material is folded so that the phases containing the fusible fibers are in contact. Typically, the folded web material passes between opposing, movable surfaces such as dies, jaws or rollers that are heated to a predetermined temperature. Actuation of the surfaces toward each other provides the required pressure and heat to the folded web material to flow and fuse the touching fusible fibers and create a heat seal seam joining the layers of web material
The surface of the second phase functions to prevent buildup of the melted polymeric fibers to the heated surfaces of the dies, jaws or rollers. It is important that the heated surfaces remain substantially free of adherent polymeric fibers to ensure proper function of the heat and pressure type sealing equipment.
It is known to use thermoplastic nonwoven materials formed by spunbonding or meltblowing for specialized sealing applications. Most of the specialized sealing equipment for such materials uses ultrasonic bonding of the contacting web materials in place of application of heat and pressure. Typically, use of spunbonded or meltblown web materials with conventional heat seal equipment leads to undesirable thermoplastic material buildup on the heated surfaces. While ultrasonic bonding avoids the material buildup problems associated with the use of conventional heat and pressure type sealing equipment and thermoplastic spunbonded materials, it is less efficient than conventional heat-seal techniques. In the high speed preparation of mass produced articles such as infusion packages, ultrasonic bonding is slower and less cost effective than conventional heat-sealing techniques and requires modification of existing equipment and processes. Additionally, known spunbonded and meltblown web materials present problems of limpness, tracking and cutting of the web material when used with conventional packing equipment having heat and pressure type sealing processes. Infusion packages made using spunbonded or meltblown materials also present problems of limpness. Further, to be acceptable for infusion packaging web materials must have a minimum combination of infusion properties and such infusion properties are not always present in spunbonded or meltblown web materials.